Video-encoding method and video-encoding apparatus using prediction units based on encoding units determined in accordance with a tree structure, and video-decoding method and video-decoding apparatus using prediction units based on encoding units determined in accordance with a tree structure

ABSTRACT

Provided are a method and apparatus for encoding a video and a method and apparatus for decoding a video. The encoding method includes: splitting a picture of the video into one or more maximum coding units; encoding the picture based on coding units according to depths which are obtained based on a partition type determined according to the depths of the coding units according to depths, determining coding units according to coded depths with respect to each of the coding units according to depths, and thus determining coding units having a tree structure; and outputting data that is encoded based on the partition type and the coding units having the tree structure, information about the coded depths and an encoding mode, and coding unit structure information indicating a size and a variable depth of a coding unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/641,418, filed Oct. 15, 2012, which is a National Stage applicationunder 35 U.S.C. §371 of PCT/KR2011/002649 filed on Apr. 13, 2011, whichclaims the benefit of U.S. Provisional Application No. 61/323,449, filedon Apr. 13, 2010 in the United States Patent and Trademark Office, thedisclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field

Apparatuses and methods consistent with exemplary embodiments relate tovideo encoding and video decoding which perform transformation between aspatial region and a transformation region.

2. Description of the Related Art

As hardware for reproducing and storing high resolution or high qualityvideo content is being developed and supplied, a need for a video codecfor effectively encoding or decoding the high resolution or high qualityvideo content is increasing. In a related art video codec, a video isencoded according to a limited encoding method based on a macroblockhaving a predetermined size. Also, the related art video codec performstransformation and inverse transformation on the macroblock by using ablock having the same size, and thus encodes and decodes video dataaccordingly.

SUMMARY

Aspects of one or more exemplary embodiments provide video encoding andvideo decoding which perform transformation between a spatial region anda transformation region by using a hierarchical prediction partition.

According to an aspect of an exemplary embodiment, there is provided amethod of decoding a video by using a prediction unit based on codingunits having a tree structure, the method including operations of:receiving a bitstream with respect to an encoded video and parsing thebitstream; extracting coding unit structure information indicating asize and a variable depth of a coding unit that is a data unit fordecoding of a picture of the video, and information about a coded depthand an encoding mode with respect to coding units having a treestructure of the picture from the bitstream; and determining the codingunits having the tree structure based on the coding unit structureinformation and the information about the coded depth and the encodingmode, determining a partition type based on a depth of a current codingunit, and decoding the picture based on the coding units and thepartition type.

According to an aspect of another exemplary embodiment, there isprovided a method of decoding a video by using a prediction unit basedon coding units having a tree structure, the method including operationsof: receiving a bitstream with respect to an encoded video and parsingthe bitstream; extracting coding unit structure information indicating asize and a variable depth of a coding unit that is a data unit fordecoding of a picture of the video, and information about a coded depthand an encoding mode with respect to coding units having a treestructure of the picture from the bitstream; and determining the codingunits having the tree structure based on the coding unit structureinformation and the information about the coded depth and the encodingmode, determining a partition type based on a depth of a current codingunit, and decoding the picture based on the coding units and thepartition type.

The partition type may include a data unit having the same size as thecurrent coding unit, and a partial data unit obtained by splitting oneof a height and a width of the current coding unit.

According to an aspect of another exemplary embodiment, there isprovided a method of encoding a video by using a prediction unit basedon coding units having a tree structure, the method including operationsof: splitting a picture of the video into one or more maximum codingunits that are coding units having a maximum size; encoding the picturebased on coding units according to depths which are obtained byhierarchically splitting each of the one or more maximum coding unitsaccording to depths in each of the one or more maximum coding units andbased on a partition type determined according to the depths of thecoding units according to depths, determining coding units according tocoded depths with respect to each of the coding units according todepths, and thus determining coding units having a tree structure; andoutputting data that is encoded based on the partition type and thecoding units having the tree structure, information about the codeddepths and an encoding mode, and coding unit structure informationindicating a size and a variable depth of a coding unit.

According to an aspect of another exemplary embodiment, there isprovided a video decoding apparatus including a video decoding processorand using a prediction unit based on coding units having a treestructure, the video decoding apparatus including: a receiver forreceiving a bitstream with respect to an encoded video, and then parsingthe bitstream; an extractor for extracting coding unit structureinformation indicating a size and a variable depth of a coding unit thatis a data unit for decoding of a picture of the video, and informationabout a coded depth and an encoding mode with respect to coding unitshaving a tree structure of the picture from the bitstream; and a decoderfor determining the coding units having the tree structure based on thecoding unit structure information and the information about the codeddepth and the encoding mode, determining a partition type based on adepth of a current coding unit, and decoding the picture based on thecoding units and the partition type, in associated with the videodecoding processor.

According to an aspect of another exemplary embodiment, there isprovided a video encoding apparatus including a video encoding processorand using a prediction unit based on coding units having a treestructure, the video encoding apparatus including: a maximum coding unitsplitter for splitting a picture of a video into one or more maximumcoding units that are coding units having a maximum size; a coding unitdeterminer for encoding the picture based on coding units according todepths which are obtained by hierarchically splitting each of the one ormore maximum coding units according to depths in each of the one or moremaximum coding units and based on a partition type determined accordingto the depths of the coding units according to depths, determiningcoding units according to coded depths with respect to each of thecoding units according to depths, and thus determining coding unitshaving a tree structure, in associated with the video encodingprocessor; and an output unit for outputting data that is encoded basedon the partition type and the coding units having the tree structure,information about the coded depths and an encoding mode, and coding unitstructure information indicating a size and a variable depth of a codingunit.

According to an aspect of another exemplary embodiment, there isprovided a computer-readable recording medium having recorded thereon aprogram for executing the method of encoding a video, by using acomputer.

According to an aspect of another exemplary embodiment, there isprovided a computer-readable recording medium having recorded thereon aprogram for executing the method of decoding a video, by using acomputer.

According to aspects of one or more exemplary embodiments, an imagecompression efficiency may be increased since a coding unit ishierarchically adjusted while considering characteristics of an imagewhile increasing a maximum size of a coding unit while considering asize of the image. Since an encoder transmits coded video data withinformation about a coded depth and an encoding mode, a decoder maydecode each piece of encoded image data after determining at least onecoded depth according to coding units having a tree structure, so thatencoding and decoding efficiency of an image may be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an apparatus for encoding a video by usinga prediction unit based on coding units having a tree structureaccording to an exemplary embodiment;

FIG. 2 is a block diagram of an apparatus for decoding a video by usinga prediction unit based on coding units having a tree structure,according to an exemplary embodiment;

FIG. 3 is a diagram for describing a concept of coding units accordingto an exemplary embodiment;

FIG. 4 is a block diagram of an image encoder based on coding unitsaccording to an exemplary embodiment;

FIG. 5 is a block diagram of an image decoder based on coding unitsaccording to an exemplary embodiment;

FIG. 6 is a diagram illustrating deeper coding units according todepths, and partitions according to an exemplary embodiment;

FIG. 7 is a diagram for describing a relationship between a coding unitand transformation units, according to an exemplary embodiment;

FIG. 8 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment;

FIG. 9 is a diagram of deeper coding units according to depths,according to an exemplary embodiment;

FIGS. 10 through 12 are diagrams for describing a relationship betweencoding units, prediction units, and transformation units, according toan exemplary embodiment;

FIG. 13 is a diagram for describing a relationship between a codingunit, a prediction unit or a partition, and a transformation unit,according to encoding mode information of Table 1;

FIG. 14 is a flowchart illustrating a method of encoding a video byusing a prediction unit based on coding units having a tree structure,according to an exemplary embodiment;

FIG. 15 is a flowchart illustrating a method of decoding a video byusing a prediction unit based on coding units having a tree structure,according to an exemplary embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments will be described more fully withreference to the accompanying drawings, in which like reference numeralsrefer to like elements throughout. In the current description, the term‘image’ may collectively indicate not only a still image but also amoving picture such as video.

Hereinafter, apparatuses and methods of encoding and decoding a video byusing a prediction unit based on coding units having a tree structurewill be described in detail with reference to FIGS. 1 through 15.

FIG. 1 is a block diagram of an apparatus for encoding a video by usinga prediction unit based on coding units having a tree structure 100according to an exemplary embodiment.

The apparatus for encoding a video by using a prediction unit based oncoding units having a tree structure 100 includes a maximum coding unitsplitter 110, a coding unit determiner 120, and an output unit 130.Hereinafter, for convenience of description, the apparatus for encodinga video by using a prediction unit based on coding units having a treestructure 100 is referred to as ‘video encoding apparatus 100’.

The maximum coding unit splitter 110 may split a current picture basedon a maximum coding unit for the current picture of an image. If thecurrent picture is larger than the maximum coding unit, image data ofthe current picture may be split into the at least one maximum codingunit. The maximum coding unit according to an exemplary embodiment maybe a data unit having a size of 32×32, 64×64, 128×128, 256×256, etc.,wherein a shape of the data unit is a square having a width and lengthin squares of 2. The image data may be output to the coding unitdeterminer 120 according to the at least one maximum coding unit.

A coding unit according to an exemplary embodiment may be characterizedby a maximum size and a depth. The depth denotes a number of times thecoding unit is spatially split from the maximum coding unit, and as thedepth deepens, deeper coding units according to depths may be split fromthe maximum coding unit to a minimum coding unit. A depth of the maximumcoding unit is an uppermost depth and a depth of the minimum coding unitis a lowermost depth. Since a size of a coding unit corresponding toeach depth decreases as the depth of the maximum coding unit deepens, acoding unit corresponding to an upper depth may include a plurality ofcoding units corresponding to lower depths.

As described above, the image data of the current picture is split intothe maximum coding units according to a maximum size of the coding unit,and each of the maximum coding units may include deeper coding unitsthat are split according to depths. Since the maximum coding unitaccording to an exemplary embodiment is split according to depths, theimage data of a spatial domain included in the maximum coding unit maybe hierarchically classified according to depths.

A maximum depth and a maximum size of a coding unit, which limit thetotal number of times a height and a width of the maximum coding unitare hierarchically split, may be predetermined.

The coding unit determiner 120 encodes at least one split regionobtained by splitting a region of the maximum coding unit according todepths, and determines a depth to output a finally encoded image dataaccording to the at least one split region. In other words, the codingunit determiner 120 determines a coded depth by encoding the image datain the deeper coding units according to depths, according to the maximumcoding unit of the current picture, and selecting a depth having theleast encoding error. Thus, the encoded image data of the coding unitcorresponding to the determined coded depth is finally output. Also, thecoding units corresponding to the coded depth may be regarded as encodedcoding units.

The determined coded depth and the encoded image data according to thedetermined coded depth are output to the output unit 130.

The image data in the maximum coding unit is encoded based on the deepercoding units corresponding to at least one depth equal to or below themaximum depth, and results of encoding the image data are compared basedon each of the deeper coding units. A depth having the least encodingerror may be selected after comparing encoding errors of the deepercoding units. At least one coded depth may be selected for each maximumcoding unit.

The size of the maximum coding unit is split as a coding unit ishierarchically split according to depths, and as the number of codingunits increases. Also, even if coding units correspond to same depth inone maximum coding unit, it is determined whether to split each of thecoding units corresponding to the same depth to a lower depth bymeasuring an encoding error of the image data of the each coding unit,separately. Accordingly, even when image data is included in one maximumcoding unit, the image data is split to regions according to the depthsand the encoding errors may differ according to regions in the onemaximum coding unit, and thus the coded depths may differ according toregions in the image data. Thus, one or more coded depths may bedetermined in one maximum coding unit, and the image data of the maximumcoding unit may be split according to coding units of at least one codeddepth.

Accordingly, the coding unit determiner 120 may determine coding unitshaving a tree structure included in the maximum coding unit. The ‘codingunits having a tree structure’ according to an exemplary embodimentinclude coding units corresponding to a depth determined to be the codeddepth, from among all deeper coding units included in the maximum codingunit. A coding unit of a coded depth may be hierarchically determinedaccording to depths in the same region of the maximum coding unit, andmay be independently determined in different regions. Similarly, a codeddepth in a current region may be independently determined from a codeddepth in another region.

A maximum depth according to an exemplary embodiment is an index relatedto the number of splitting times from a maximum coding unit to a minimumcoding unit. A maximum depth according to an exemplary embodiment maydenote the total number of splitting times from the maximum coding unitto the minimum coding unit. For example, when a depth of the maximumcoding unit is 0, a depth of a coding unit, in which the maximum codingunit is split once, may be set to 1, and a depth of a coding unit, inwhich the maximum coding unit is split twice, may be set to 2. Here, ifthe minimum coding unit is a coding unit in which the maximum codingunit is split four times, 5 depth levels of depths 0, 1, 2, 3 and 4exist, and thus the maximum depth may be set to 4.

Prediction encoding and transformation may be performed according to themaximum coding unit. The prediction encoding and the transformation arealso performed based on the deeper coding units according to a depthequal to or depths less than the maximum depth, according to the maximumcoding unit. Transformation may be performed according to method offrequency transformation, orthogonal transformation or integertransformation.

Since the number of deeper coding units increases whenever the maximumcoding unit is split according to depths, encoding including theprediction encoding and the transformation is performed on all of thedeeper coding units generated as the depth deepens. For convenience ofdescription, the prediction encoding and the transformation will now bedescribed based on a coding unit of a current depth, in a maximum codingunit.

The video encoding apparatus 100 may variously select a size or shape ofa data unit for encoding the image data. In order to encode the imagedata, operations, such as prediction encoding, transformation, andentropy encoding, are performed, and at this time, the same data unitmay be used for all operations or different data units may be used foreach operation.

For example, the video encoding apparatus 100 may select not only acoding unit for encoding the image data, but also a data unit differentfrom the coding unit so as to perform the prediction encoding on theimage data in the coding unit.

In order to perform prediction encoding in the maximum coding unit, theprediction encoding may be performed based on a coding unitcorresponding to a coded depth, i.e., based on a coding unit that is nolonger split to coding units corresponding to a lower depth.Hereinafter, the coding unit that is no longer split and becomes a basisunit for prediction encoding will now be referred to as a ‘predictionunit’. A partition obtained by splitting the prediction unit may includea prediction unit or a data unit obtained by splitting at least one of aheight and a width of the prediction unit.

For example, when a coding unit of 2N×2N (where N is a positive integer)is no longer split and becomes a prediction unit of 2N×2N, and a size ofa partition may be 2N×2N, 2N×N, or N×2N. Examples of a partition typeinclude symmetrical partitions that are obtained by symmetricallysplitting a height or width of the prediction unit, partitions obtainedby asymmetrically splitting the height or width of the prediction unit,such as 1:n or n:1, partitions that are obtained by geometricallysplitting the prediction unit, and partitions having arbitrary shapes.

A size of the partition type or the prediction unit of the coding unitmay be determined according to whether split is performed on a currentcoding unit with a current depth or a lower depth.

When the partition type of the current coding is a symmetrical partitiontype, the symmetrical partition type of the current coding unit mayinclude a partition having the same size as the current coding unit, anda partition obtained by dividing a height or width of the current codingunit by two. That is, a symmetrical partition type of a coding unithaving a size of 2N×2N may include partitions of 2N×2N, 2N×N, or N×2N.

When the current coding unit is no longer split into coding units of alower depth, the symmetrical partition type of the current coding unitmay include partitions having the same size as the coding units of thelower depth. That is, when the current coding unit is a minimum codingunit that cannot be split into coding units of a lower depth and that isfrom among current maximum coding units, the symmetrical partition typeof the current coding unit may include not only the partitions of 2N×2N,2N×N, and N×2N but also may include a partition having a size of N×N.

Similarly, when the current coding unit is a coding unit of a lowestdepth from among the current maximum coding units, the symmetricalpartition type of the current coding unit may include not only thepartitions of 2N×2N, 2N×N, and N×2N but also may include a partitionhaving a size of N×N.

For example, when a coding unit having a current depth and a size of2N×2N is split once and thus is divided into coding units having a lowerdepth and a size of N×N, intra prediction and inter prediction may beperformed on the coding unit having the size of N×N by using thepartition having the size of N×N. Thus, in order to avoid repetition ofan unnecessary process, in a structure of hierarchical coding unitsaccording to the present exemplary embodiment, a partition type having asize of N×N may not be set to the coding unit having the size of 2N×2N.

However, when the current coding unit having the size of 2N×2N is theminimum coding unit, the current coding unit is no longer split intocoding units having a size of N×N, so that the inter prediction or theintra prediction may be performed on the current coding unit by usingpartitions having a size of N×N. Thus, the partition type of the minimumcoding unit having the size of 2N×2N may include the partitions of2N×2N, 2N×N, N×2N, and N×N.

A prediction mode of the prediction unit may be at least one of an intramode, a inter mode, and a skip mode. For example, prediction encoding inthe intra mode and the inter mode may be performed on the partition of2N×2N, 2N×N, or N×2N.

That is, in at least one of cases in which the current coding unit isnot the minimum coding unit, in which the current coding unit is splitinto coding units of a lower depth, and in which the current coding unitis not the coding unit of a lowest depth from among the current maximumcoding units, the inter prediction and the intra prediction which areperformed by using the partition of N×N may be skipped.

However, when the current coding unit is the minimum coding unit, sincethe intra prediction and the inter prediction cannot be performed on acoding unit of a lower depth, the inter prediction and the intraprediction may be performed on the minimum coding unit by using thepartitions of 2N×2N, 2N×N, N×2N, and N×N.

Also, the skip mode may be performed only on the partition of 2N×2N. Theencoding is independently performed on one prediction unit in a codingunit, thereby selecting a prediction mode causing a least encodingerror.

The video encoding apparatus 100 may also perform the transformation onthe image data in a coding unit based not only on the coding unit forencoding the image data, but also based on a data unit that is differentfrom the coding unit.

In order to perform the transformation in the coding unit, thetransformation may be performed based on a transformation unit having asize smaller than or equal to the coding unit. For example, thetransformation unit for the transformation may include a transformationunit for an intra mode and a transformation unit for an inter mode.

Similarly to the coding unit having a tree structure, the transformationunit in the coding unit may be recursively split into smaller sizedregions. Thus, residual data in the coding unit may be split accordingto the transformation having the tree structure according totransformation depths.

A transformation depth indicating the number of splitting times to reachthe transformation unit by splitting the height and width of the codingunit may also be set in the transformation unit. For example, in acurrent coding unit of 2N×2N, a transformation depth may be 0 when thesize of a transformation unit is also 2N×2N, may be 1 when the size ofthe transformation unit is thus N×N, and may be 2 when the size of thetransformation unit is thus N/2×N/2. That is, the transformation unitmay be set according to a hierarchical tree structure according to thehierarchical characteristics of transformation depths.

Encoding information according to coding units corresponding to a codeddepth uses not only information about the coded depth, but also aboutinformation related to prediction encoding and transformation.Accordingly, the coding unit determiner 120 not only determines a codeddepth having a least encoding error, but also determines a partitiontype in a prediction unit, a prediction mode according to predictionunits, and a size of a transformation unit for transformation.

Coding units according to a tree structure in a maximum coding unit anda method of determining a partition, according to exemplary embodiments,will be described in detail below with reference to FIGS. 3 through 13.

The coding unit determiner 120 may measure an encoding error of deepercoding units according to depths by using Rate-Distortion Optimizationbased on Lagrangian multipliers.

The output unit 130 outputs the image data of the maximum coding unit,which is encoded based on the at least one coded depth determined by thecoding unit determiner 120, and information about the encoding modeaccording to the coded depth, in bitstreams.

The encoded image data may be obtained by encoding residual data of animage.

The information about the encoding mode according to coded depth mayinclude information about the coded depth, about the partition type inthe prediction unit, the prediction mode, and the size of thetransformation unit.

The information about the coded depth may be defined by using splitinformation according to depths, which indicates whether encoding isperformed on coding units of a lower depth instead of a current depth.If the current depth of the current coding unit is the coded depth,image data in the current coding unit is encoded and output, and thusthe split information may be defined not to split the current codingunit to a lower depth. Alternatively, if the current depth of thecurrent coding unit is not the coded depth, the encoding is performed onthe coding unit of the lower depth, and thus the split information maybe defined to split the current coding unit to obtain the coding unitsof the lower depth.

If the current depth is not the coded depth, encoding is performed onthe coding unit that is split into the coding unit of the lower depth.Since at least one coding unit of the lower depth exists in one codingunit of the current depth, the encoding is repeatedly performed on eachcoding unit of the lower depth, and thus the encoding may be recursivelyperformed for the coding units having the same depth.

Since the coding units having a tree structure are determined for onemaximum coding unit, and information about at least one encoding mode isdetermined for a coding unit of a coded depth, information about atleast one encoding mode may be determined for one maximum coding unit.Also, a coded depth of the image data of the maximum coding unit may bedifferent according to locations since the image data is hierarchicallysplit according to depths, and thus information about the coded depthand the encoding mode may be set for the image data.

Accordingly, the output unit 130 may assign encoding information about acorresponding coded depth and an encoding mode to at least one of thecoding unit, the prediction unit, and a minimum unit included in themaximum coding unit. The output unit 130 may insert information about acorresponding coded depth and a corresponding coding mode into a headerof a bitstream to transmit encoded video data, a Sequence Parameter Set(SPS) or a Picture Parameter Set (PPS), and may output them.

The minimum unit according to an exemplary embodiment is a rectangulardata unit obtained by splitting the minimum coding unit constituting thelowermost depth by 4. The minimum unit according to an exemplaryembodiment may be a maximum rectangular data unit that may be includedin all of the coding units, prediction units, partition units, andtransformation units included in the maximum coding unit.

For example, the encoding information output through the output unit 130may be classified into encoding information according to coding units,and encoding information according to prediction units. The encodinginformation according to the coding units may include the informationabout the prediction mode and about the size of the partitions. Theencoding information according to the prediction units may includeinformation about an estimated direction of an inter mode, about areference image index of the inter mode, about a motion vector, about achroma component of an intra mode, and about an interpolation method ofthe intra mode.

Also, coding unit structure information about a size and a variabledepth of the coding unit defined according to sequences, pictures,slices, or GOPs may be inserted into a SPS, a PPS, or a header of abitstream.

The variable depth may indicate not only an allowed maximum depth ofcurrent coding units having a tree structure but also may indicate alowest depth of a coding unit having a minimum size, the number of depthlevels, or depth variation.

The number of depth levels may indicate the number of the depth levelsof deeper coding units according to depths that may exist in the currentcoding units having the tree structure. The depth variation may indicatethe number of variation of the deeper coding units according to depthsthat may exist in the current coding units having the tree structure.

Information about the variable depth may be set according to sequences,pictures, slices, or GOPs. That is, the information about the variabledepth and information about the maximum size or information about theminimum size of the coding unit from among the current coding unitshaving the tree structure may be set for each of data units of thesequences, the pictures, the slices, or the GOPs.

Thus, the output unit 130 may include coding information including, ascoding unit structure information, at least two of the information aboutthe variable depth, the information about the maximum size of the codingunit, and the information about the minimum size of the coding unit, mayinsert the coding information into a header of a bitstream, i.e., a SPSor a PPS, and then may output the bitstream. The variable depth, themaximum size, and the minimum size of the coding unit are determinedaccording to sequences, pictures, slices, or GOPs, respectively. Inaddition, the coding information output from the output unit 130 mayinclude transformation indexes. Transformation index information mayindicate information about a structure of a transformation unit that isused to transform the current coding unit. The transformation indexinformation may indicate whether a current transformation unit is splitinto lower-level transformation units.

In the video encoding apparatus 100, the deeper coding unit may be acoding unit obtained by dividing a height or width of a coding unit ofan upper depth, which is one level above, by two. In other words, whenthe size of the coding unit of the current depth is 2N×2N, the size ofthe coding unit of the lower depth is N×N. Also, the coding unit of thecurrent depth having the size of 2N×2N may include maximum 4 of thecoding unit of the lower depth.

Accordingly, the video encoding apparatus 100 may form the coding unitshaving the tree structure by determining coding units having an optimumshape and an optimum size for each maximum coding unit, based on thesize of the maximum coding unit and the maximum depth determinedconsidering characteristics of the current picture. Also, since encodingmay be performed on each maximum coding unit by using any one of variousprediction modes and transformations, an optimum encoding mode may bedetermined considering characteristics of the coding unit of variousimage sizes.

Thus, if an image having high resolution or large data amount is encodedin a related art macroblock, a number of macroblocks per pictureexcessively increases. Accordingly, a number of pieces of compressedinformation generated for each macroblock increases, and thus it isdifficult to transmit the compressed information and data compressionefficiency decreases. However, by using the video encoding apparatus100, image compression efficiency may be increased since a coding unitis adjusted while considering characteristics of an image whileincreasing a maximum size of a coding unit while considering a size ofthe image.

FIG. 2 is a block diagram of an apparatus for decoding a video by usinga prediction unit based on coding units according to a tree structure200, according to an exemplary embodiment.

The apparatus for decoding a video by using a prediction unit based oncoding units according to a tree structure 200 includes a receiver 210,an image data and encoding information extractor 220, and an image datadecoder 230. Hereinafter, for convenience of description, the apparatusfor decoding a video by using a prediction unit based on coding unitsaccording to a tree structure 200 is referred to as ‘video decodingapparatus 200’.

Definitions of various terms, such as a coding unit, a depth, aprediction unit, a transformation unit, and information about variousencoding modes, for various operations of the video decoding apparatus200 are identical to those described with reference to FIG. 1 and thevideo encoding apparatus 100.

The receiver 210 receives and parses a bitstream of an encoded video.The image data and encoding information extractor 220 extracts encodedimage data for each coding unit from the parsed bitstream, wherein thecoding units have a tree structure according to each maximum codingunit, and outputs the extracted image data to the image data decoder230. The image data and encoding information extractor 220 may extractcoding unit structure information about a size and a variable depth of acoding unit of a current picture, and information about a coded depthand an encoding mode from at least one of a header, an SPS, and a PPSwith respect to the current picture from the received bitstream.

The image data and encoding information extractor 220 may extract theinformation about the variable depth and one of information about anallowable maximum size and information about an allowable minimum sizeof a coding unit from among coding units having a tree structure foreach of data units of sequences, pictures, slices, or GOPs, from codinginformation. The image data decoder 230 may determine the allowablemaximum size and the allowable minimum size of the coding unit fromamong the coding units having the tree structure for each of data unitsof sequences, pictures, slices, or GOPs, by using at least two pieces ofthe information about the variable depth, the information about themaximum size of the coding unit, and the information about the minimumsize of the coding unit.

At least two pieces of the information about the variable depth, theinformation about the maximum size of the coding unit, and theinformation about the minimum size of the coding unit, which aredetermined for each of pictures, slices, or GOPs, may be extracted fromthe coding information, and an allowable maximum size and an allowableminimum size of a current data unit may be determined based on the readinformation. Also, the image data and encoding information extractor 220extracts information about a coded depth and an encoding mode for thecoding units having a tree structure according to each maximum codingunit, from the parsed bitstream. The extracted information about thecoded depth and the encoding mode is output to the image data decoder230. In other words, the image data in a bit stream is split into themaximum coding unit so that the image data decoder 230 decodes the imagedata for each maximum coding unit.

The information about the coded depth and the encoding mode according tothe maximum coding unit may be set for information about at least onecoding unit corresponding to the coded depth, and information about anencoding mode may include information about a partition type of acorresponding coding unit corresponding to the coded depth, about aprediction mode, and a size of a transformation unit. Also, splittinginformation according to depths may be extracted as the informationabout the coded depth.

Also, the image data decoder 230 may read information abouttransformation indexes from the coding information that is extractedfrom the parsed bitstream. The image data decoder 230 may configure atransformation unit of the current coding unit based on image data andtransformation index information extracted by the image data andencoding information extractor 220, may perform inverse transformationof the current coding unit based on the transformation unit, and thusmay decode encoded data. As a result of decoding the coding units, thecurrent picture may be restored.

The information about the coded depth and the encoding mode according toeach maximum coding unit extracted by the image data and encodinginformation extractor 220 is information about a coded depth and anencoding mode determined to generate a minimum encoding error when anencoder, such as the video encoding apparatus 100, repeatedly performsencoding for each deeper coding unit according to depths according toeach maximum coding unit. Accordingly, the video decoding apparatus 200may restore an image by decoding the image data according to a codeddepth and an encoding mode that generates the minimum encoding error.

Since encoding information about the coded depth and the encoding modemay be assigned to a predetermined data unit from among a correspondingcoding unit, a prediction unit, and a minimum unit, the image data andencoding information extractor 220 may extract the information about thecoded depth and the encoding mode according to the predetermined dataunits. The predetermined data units to which the same information aboutthe coded depth and the encoding mode is assigned may be inferred to bethe data units included in the same maximum coding unit.

The image data decoder 230 restores the current picture by decoding theimage data in each maximum coding unit based on the information aboutthe coded depth and the encoding mode according to the maximum codingunits. In other words, the image data decoder 230 may decode the encodedimage data based on the extracted information about the partition type,the prediction mode, and the transformation unit for each coding unitfrom among the coding units having the tree structure included in eachmaximum coding unit. A decoding process may include a predictionincluding intra prediction and motion compensation, and an inversetransformation. Inverse transformation may be performed according tomethod of inverse orthogonal transformation or inverse integertransformation.

The image data decoder 230 may perform intra prediction or motioncompensation according to a partition and a prediction mode of eachcoding unit, based on the information about the partition type and theprediction mode of the prediction unit of the coding unit according tocoded depths.

Also, the image data decoder 230 may perform inverse transformationaccording to each transformation unit in the coding unit, by reading thetransformation unit according to a tree structure, and the informationabout the size of the transformation unit of the coding unit accordingto coded depths, so as to perform the inverse transformation accordingto maximum coding units.

The image data decoder 230 may determine at least one coded depth of acurrent maximum coding unit by using split information according todepths. If the split information indicates that image data is no longersplit in the current depth, the current depth is a coded depth.Accordingly, the image data decoder 230 may decode encoded data of atleast one coding unit corresponding to the each coded depth in thecurrent maximum coding unit by using the information about the partitiontype of the prediction unit, the prediction mode, and the size of thetransformation unit for each coding unit corresponding to the codeddepth, and output the image data of the current maximum coding unit.

In other words, data units containing the encoding information includingthe same split information may be gathered by observing the encodinginformation set assigned for the predetermined data unit from among thecoding unit, the prediction unit, and the minimum unit, and the gathereddata units may be considered to be one data unit to be decoded by theimage data decoder 230 in the same encoding mode.

The video decoding apparatus 200 may obtain information about at leastone coding unit that generates the minimum encoding error when encodingis recursively performed for each maximum coding unit, and may use theinformation to decode the current picture. In other words, the codingunits having the tree structure determined to be the optimum codingunits in each maximum coding unit may be decoded. Also, the maximum sizeof coding unit is determined considering resolution and an amount ofimage data.

Accordingly, even if image data has high resolution and a large amountof data, the image data may be efficiently decoded and restored by usinga size of a coding unit and an encoding mode, which are adaptivelydetermined according to characteristics of the image data, by usinginformation about an optimum encoding mode received from an encoder.

A method of determining coding units having a tree structure, aprediction unit, and a transformation unit, according to an exemplaryembodiment, will now be described with reference to FIGS. 3 through 13.

FIG. 3 is a diagram for describing a concept of coding units accordingto an exemplary embodiment.

A size of a coding unit may be expressed in width×height, and may be64×64, 32×32, 16×16, and 8×8.

In video data 310, a resolution is 1920×1080, a maximum size of a codingunit is 64, and a maximum depth is 2. In video data 320, a resolution is1920×1080, a maximum size of a coding unit is 64, and a maximum depth is3. In video data 330, a resolution is 352×288, a maximum size of acoding unit is 16, and a maximum depth is 1. The maximum depth shown inFIG. 3 denotes a total number of splits from a maximum coding unit to aminimum decoding unit.

If a resolution is high or a data amount is large, a maximum size of acoding unit may be large so as to not only increase encoding efficiencybut also to accurately reflect characteristics of an image. Accordingly,the maximum size of the coding unit of the video data 310 and 320 havingthe higher resolution than the video data 330 may be 64.

Since the maximum depth of the video data 310 is 2, coding units 315 ofthe vide data 310 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32 and 16 sincedepths are deepened to two levels by splitting the maximum coding unittwice. Meanwhile, since the maximum depth of the video data 330 is 1,coding units 335 of the video data 330 may include a maximum coding unithaving a long axis size of 16, and coding units having a long axis sizeof 8 since depths are deepened to one level by splitting the maximumcoding unit once.

Since the maximum depth of the video data 320 is 3, coding units 325 ofthe video data 320 may include a maximum coding unit having a long axissize of 64, and coding units having long axis sizes of 32, 16, and 8since the depths are deepened to 3 levels by splitting the maximumcoding unit three times. As a depth deepens, detailed information may beprecisely expressed.

Partition types of having sizes of 64×64, 64×32, and 32×64 may be set toa coding unit having a size of 64×64. Since the coding unit having thesize of 64×64 is not a minimum decoding unit with respect to a pluralityof pieces of the video data 310, 320, and 330, a partition type having asize of 32×32 may not be set.

Partition types of having sizes of 32×32, 32×16, and 16×32 may be set toa coding unit having a size of 32×32. Since the coding unit having thesize of 32×32 is not a minimum decoding unit with respect to a pluralityof pieces of the video data 310, 320, and 330, a partition type having asize of 16×16 may not be set.

Partition types of having sizes of 16×16, 16×8, and 8×16 may be set to acoding unit having a size of 16×16. Since the coding unit having thesize of 16×16 is a minimum decoding unit with respect to the video data310, a partition type having a size of 8×8 may be set. However, thecoding unit having the size of 16×16 is not a minimum decoding unit withrespect to a plurality of pieces of the video data 320 and 330, thepartition type having the size of 8×8 may not be set.

In this regard, since the coding unit having the size of 8×8 is aminimum decoding unit with respect to a plurality of pieces of the videodata 310, 320, and 330, not only the partitions types having the size of8×8, 8×4, and 4×8 but also a partition type having a size of 4×4 mayalso be set.

FIG. 4 is a block diagram of an image encoder 400 based on coding units,according to an exemplary embodiment.

The image encoder 400 performs operations of the coding unit determiner120 of the video encoding apparatus 100 to encode image data. In otherwords, an intra predictor 410 performs intra prediction on coding unitsin an intra mode, from among a current frame 405, and a motion estimator420 and a motion compensator 425 performs inter estimation and motioncompensation on coding units in an inter mode from among the currentframe 405 by using the current frame 405, and a reference frame 495.

Data output from the intra predictor 410, the motion estimator 420, andthe motion compensator 425 is output as a quantized transformationcoefficient through a transformer 430 and a quantizer 440. The quantizedtransformation coefficient is restored as data in a spatial domainthrough an inverse quantizer 460 and an inverse transformer 470, and therestored data in the spatial domain is output as the reference frame 495after being post-processed through a deblocking unit 480 and a loopfiltering unit 490. The quantized transformation coefficient may beoutput as a bitstream 455 through an entropy encoder 450.

In order for the image encoder 400 to be applied in the video encodingapparatus 100, all elements of the image encoder 400, i.e., the intrapredictor 410, the motion estimator 420, the motion compensator 425, thetransformer 430, the quantizer 440, the entropy encoder 450, the inversequantizer 460, the inverse transformer 470, the deblocking unit 480, andthe loop filtering unit 490 perform operations based on each coding unitfrom among coding units having a tree structure while considering themaximum depth of each maximum coding unit.

Specifically, the intra predictor 410, the motion estimator 420, and themotion compensator 425 determines partitions and a prediction mode ofeach coding unit from among the coding units having a tree structurewhile considering the maximum size and the maximum depth of a currentmaximum coding unit, and the transformer 430 determines the size of thetransformation unit in each coding unit from among the coding unitshaving a tree structure.

FIG. 5 is a block diagram of an image decoder 500 based on coding units,according to an exemplary embodiment.

A parser 510 parses encoded image data to be decoded and informationabout encoding for decoding from a bitstream 505. The encoded image datais output as inverse quantized data through an entropy decoder 520 andan inverse quantizer 530, and the inverse quantized data is restored toimage data in a spatial domain through an inverse transformer 540.

An intra predictor 550 performs intra prediction on coding units in anintra mode with respect to the image data in the spatial domain, and amotion compensator 560 performs motion compensation on coding units inan inter mode by using a reference frame 585.

The image data in the spatial domain, which passed through the intrapredictor 550 and the motion compensator 560, may be output as arestored frame 595 after being post-processed through a deblocking unit570 and a loop filtering unit 580. Also, the image data that ispost-processed through the deblocking unit 570 and the loop filteringunit 580 may be output as the reference frame 585.

In order to decode the image data in the image data decoder 230 of thevideo decoding apparatus 200, the image decoder 500 may performoperations that are performed after the parser 510.

In order for the image decoder 500 to be applied in the video decodingapparatus 200, all elements of the image decoder 500, i.e., the parser510, the entropy decoder 520, the inverse quantizer 530, the inversetransformer 540, the intra predictor 550, the motion compensator 560,the deblocking unit 570, and the loop filtering unit 580 performoperations based on coding units having a tree structure for eachmaximum coding unit.

Specifically, the intra prediction 550 and the motion compensator 560perform operations based on partitions and a prediction mode for each ofthe coding units having a tree structure, and the inverse transformer540 perform operations based on a size of a transformation unit for eachcoding unit.

FIG. 6 is a diagram illustrating deeper coding units according todepths, and partitions, according to an exemplary embodiment.

The video encoding apparatus 100 and the video decoding apparatus 200use hierarchical coding units so as to consider characteristics of animage. A maximum height, a maximum width, and a maximum depth of codingunits may be adaptively determined according to the characteristics ofthe image, or may be differently set by a user. Sizes of deeper codingunits according to depths may be determined according to thepredetermined maximum size of the coding unit.

In a hierarchical structure 600 of coding units, according to anexemplary embodiment, the maximum height and the maximum width of thecoding units are each 64, and the maximum depth is 3. Here, the maximumdepth indicates a total number of splits of the coding unit according todepths from a maximum coding unit to a minimum decoding unit. Since adepth deepens along a vertical axis of the hierarchical structure 600, aheight and a width of the deeper coding unit are each split. Also, aprediction unit and partitions, which are bases for prediction encodingof each deeper coding unit, are shown along a horizontal axis of thehierarchical structure 600.

In other words, a coding unit 610 is a maximum coding unit in thehierarchical structure 600, wherein a depth is 0 and a size, i.e., aheight by width, is 64×64. The depth deepens along the vertical axis,and a coding unit 620 having a size of 32×32 and a depth of 1, a codingunit 630 having a size of 16×16 and a depth of 2, and a coding unit 640having a size of 8×8 and a depth of 3 exist. The coding unit 640 havinga size of 8×8 and a depth of 3 is a minimum coding unit.

The prediction unit and the partitions of a coding unit are arrangedalong the horizontal axis according to each depth. In other words, ifthe coding unit 610 having the size of 64×64 and the depth of 0 is aprediction unit, the prediction unit may be split into partitionsincluded in the coding unit 610, i.e., a partition 610 having a size of64×64, partitions 612 having the size of 64×32, and partitions 614having the size of 32×64. Since the coding unit 610 having the size of64×64 is not a minimum coding unit, partitions having a size of 32×32are not set.

Similarly, a prediction unit of the coding unit 620 having the size of32×32 and the depth of 1 may be split into partitions included in thecoding unit 620, i.e., a partition 620 having a size of 32×32,partitions 622 having a size of 32×16, and partitions 624 having a sizeof 16×32. Since the coding unit 620 having the size of 32×32 is not aminimum coding unit, partitions having a size of 16×16 are not set.

Similarly, a prediction unit of the coding unit 630 having the size of16×16 and the depth of 2 may be split into partitions included in thecoding unit 630, i.e., a partition having a size of 16×16 included inthe coding unit 630, partitions 632 having a size of 16×8, andpartitions 634 having a size of 8×16. Since the coding unit 630 havingthe size of 16×16 is not a minimum coding unit, partitions having a sizeof 8×8 are not set.

Finally, a prediction unit of the coding unit 640 having the size of 8×8and the depth of 3 is a minimum coding unit and has a lowest depth andthus may be split into partitions included in the coding unit 640, i.e.,a partition having a size of 8×8 included in the coding unit 640,partitions 642 having a size of 8×4, partitions 644 having a size of4×8, and partitions 646 having a size of 4×4.

In order to determine the at least one coded depth of the coding unitsconstituting the maximum coding unit 610, the coding unit determiner 120of the video encoding apparatus 100 performs encoding for coding unitscorresponding to each depth included in the maximum coding unit 610.

A number of deeper coding units according to depths including data inthe same range and the same size increases as the depth deepens. Forexample, four coding units corresponding to a depth of 2 are used tocover data that is included in one coding unit corresponding to a depthof 1. Accordingly, in order to compare encoding results of the same dataaccording to depths, the coding unit corresponding to the depth of 1 andfour coding units corresponding to the depth of 2 are each encoded.

In order to perform encoding for a current depth from among the depths,a least encoding error may be selected for the current depth byperforming encoding for each prediction unit in the coding unitscorresponding to the current depth, along the horizontal axis of thehierarchical structure 600. Alternatively, the minimum encoding errormay be searched for by comparing the least encoding errors according todepths, by performing encoding for each depth as the depth deepens alongthe vertical axis of the hierarchical structure 600. A depth and apartition having the minimum encoding error in the coding unit 610 maybe selected as the coded depth and a partition type of the coding unit610.

FIG. 7 is a diagram for describing a relationship between a coding unit710 and transformation units 720, according to an exemplary embodiment.

The video encoding apparatus 100 or 200 encodes or decodes an imageaccording to coding units having sizes smaller than or equal to amaximum coding unit for each maximum coding unit. Sizes oftransformation units for transformation during encoding may be selectedbased on data units that are not larger than a corresponding codingunit.

For example, in the video encoding apparatus 100 or 200, if a size ofthe coding unit 710 is 64×64, transformation may be performed by usingthe transformation units 720 having a size of 32×32.

Also, data of the coding unit 710 having the size of 64×64 may beencoded by performing the transformation on each of the transformationunits having the size of 32×32, 16×16, 8×8, and 4×4, which are smallerthan 64×64, and then a transformation unit having the least coding errormay be selected.

FIG. 8 is a diagram for describing encoding information of coding unitscorresponding to a coded depth, according to an exemplary embodiment.

The output unit 130 of the video encoding apparatus 100 may encode andtransmit information 800 about a partition type, information 810 about aprediction mode, and information 820 about a size of a transformationunit for each coding unit corresponding to a coded depth, as informationabout an encoding mode.

The information 800 indicates information about a shape of a partitionobtained by splitting a prediction unit of a current coding unit,wherein the partition is a data unit for prediction encoding the currentcoding unit. For example, a current coding unit CU_0 having a size of2N×2N may be split into any one of a partition 802 having a size of2N×2N, a partition 804 having a size of 2N×N, and a partition 806 havinga size of N×2N. Here, the information 800 about a partition type is setto indicate one of the partition 804 having a size of 2N×N and thepartition 806 having a size of N×2N. However, when the current codingunit CU_0 having a size of 2N×2N is a minimum coding unit, theinformation 800 about a partition type may include a partition 808having a size of N×N.

The information 810 indicates a prediction mode of each partition. Forexample, the information 810 may indicate a mode of prediction encodingperformed on a partition indicated by the information 800, i.e., anintra mode 812, an inter mode 814, or a skip mode 816.

The information 820 indicates a transformation unit to be based on whentransformation is performed on a current coding unit. For example, thetransformation unit may be a first intra transformation unit 822, asecond intra transformation unit 824, a first inter transformation unit826, or a second intra transformation unit 828.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information 800, 810, and820 for decoding, according to each deeper coding unit

FIG. 9 is a diagram of deeper coding units according to depths,according to an exemplary embodiment.

Split information may be used to indicate a change of a depth. The spiltinformation indicates whether a coding unit of a current depth is splitinto coding units of a lower depth.

A prediction unit 910 for prediction-encoding a coding unit 900 having adepth of 0 and a size of 2N_0×2N_0 may include partitions of a partitiontype 912 having a size of 2N_0×2N_0, a partition type 914 having a sizeof 2N_0×N_0, and a partition type 916 having a size of N_0×2N_0. FIG. 9only illustrates the partition types 912 through 916 which are obtainedby symmetrically splitting the prediction unit 910, but a partition typeis not limited thereto, and the partitions of the prediction unit 910may include asymmetrical partitions, partitions having an arbitraryshape, and partitions having a geometrical shape.

Prediction encoding is repeatedly performed on one partition having asize of 2N_0×2N_0, two partitions having a size of 2N_0×N_0, and twopartitions having a size of N_0×2N_0, according to each partition type.The prediction encoding in an intra mode and an inter mode may beperformed on the partitions having the sizes of 2N_0×2N_0, N_0×2N_0, and2N_0×N_0. The prediction encoding in a skip mode is performed only onthe partition having the size of 2N_0×2N_0.

If an encoding error is smallest in one of the partition types 912through 916 having the sizes of 2N_0×2N_0, N_0×2N_0, and 2N_0×N_0, theprediction unit 910 may not be split into a lower depth. However, if theencoding error is the smallest in coding units 930 having a size ofN_0×N_0, a depth is changed from 0 to 1 to perform split (operation920), and encoding is repeatedly performed on the coding units 930having a depth of 1 and the size of N_0×N_0 to search for a minimumencoding error.

A prediction unit 940 for prediction-encoding the coding unit 930 havinga depth of 1 and a size of 2N_1×2N_1 (=N_0×N_0) may include partitionsof a partition type 942 having a size of 2N_1×2N_1, a partition type 944having a size of 2N_1×N_1, and a partition type 946 having a size ofN_1×2N_1.

If an encoding error is the smallest in coding units 960 having a sizeof N_2×N_2, compared to encoding errors in the partitions types 942through 946 having the sizes of 2N_1×N_1, N_1×2N_1, and 2N_1×N_1, adepth is changed from 1 to 2 to perform split (operation 950), andencoding is repeatedly performed on the coding units 960, which have adepth of 2 and the size of N_2×N_2, to search for a minimum encodingerror.

When a maximum depth is d−1, a coding unit according to each depth maybe split up to when a depth becomes d−1, and split information may beencoded as up to when a depth is one of 0 to d−2. In other words, whenencoding is performed up to when the depth is d−1 after a coding unitcorresponding to a depth of d−2 is split in operation 970, a predictionunit 990 for prediction-encoding a coding unit 980 having a depth of d−1and a size of 2N_(d−1)×2N_(d−1) may include partitions of a partitiontype 992 having a size of 2N_(d−1)×2N_(d−1), a partition type 994 havinga size of 2N_(d−1)×N_(d−1), a partition type 996 having a size ofN_(d−1)×2N_(d−1), and a partition type 998 having a size ofN_(d−1)×N_(d−1). Prediction encoding may be repeatedly performed on onepartition having a size of 2N_(d−1)×2N_(d−1), two partitions having asize of 2N_(d−1)×N_(d−1), two partitions having a size ofN_(d−1)×2N_(d−1), four partitions having a size of N_(d−1)×N_(d−1) fromamong the partition types 992 through 998 to search for a partition typehaving a minimum encoding error.

Even when the partition type 998 has the minimum encoding error, since amaximum depth is d−1, a coding unit CU_(d−1) having a depth of d−1 is nolonger split to a lower depth, and a coded depth for the coding unitsconstituting a current maximum coding unit 900 is determined to be d−1and a partition type of the current maximum coding unit 900 may bedetermined to be N_(d−1)×N_(d−1). Also, since the maximum depth is d−1and a minimum coding unit 980 having a lowermost depth of d−1 is nolonger split to a lower depth, split information for the minimum codingunit 980 is not set.

Since the coding unit 900 having the depth of 0 and the size of2N_0×2N_0 and the coding unit 930 having the depth of 1 and the size of2N_1×2N_1 are not minimum coding units, the prediction unit 910 for thecoding unit 900 having the size of 2N_0×2N_0 may not include a partitiontype having a size of N_0×N_0, and the prediction unit 940 for thecoding unit 930 having the size of 2N_1×2N_1 may not include a partitiontype having a size of N_1×N_1.

However, the prediction unit 990 for prediction encoding the coding unit980 having the depth of d−1 which is a minimum coding unit may includethe partition type 998 having a size of N_(d−1)×N_(d−1).

A data unit 999 may be a ‘minimum unit’ for the current maximum codingunit. A minimum unit according to an exemplary embodiment may be arectangular data unit obtained by splitting a minimum coding unit 980 by4. By performing the encoding repeatedly, the video encoding apparatus100 may select a depth having the least encoding error by comparingencoding errors according to depths of the coding unit 900 to determinea coded depth, and set a corresponding partition type and a predictionmode as an encoding mode of the coded depth.

As such, the minimum encoding errors according to depths are compared inall of the depths of 1 through d, and a depth having the least encodingerror may be determined as a coded depth. The coded depth, the partitiontype of the prediction unit, and the prediction mode may be encoded andtransmitted as information about an encoding mode. Also, since a codingunit is split from a depth of 0 to a coded depth, only split informationof the coded depth is set to 0, and split information of depthsexcluding the coded depth is set to 1.

The image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract and use the information about thecoded depth and the prediction unit of the coding unit 900 to decode thepartition 912. The video decoding apparatus 200 may determine a depth,in which split information is 0, as a coded depth by using splitinformation according to depths, and use information about an encodingmode of the coded depth for decoding coding unit corresponding to thecoded depth.

FIGS. 10 through 12 are diagrams for describing a relationship betweencoding units 1010, prediction units 1060, and transformation units 1070,according to an exemplary embodiment.

The coding units 1010 are coding units having a tree structure,corresponding to coded depths determined by the video encoding apparatus100, in a maximum coding unit. The prediction units 1060 are partitionsof prediction units of each of the coding units 1010, and thetransformation units 1070 are transformation units of each of the codingunits 1010.

When a depth of a maximum coding unit is 0 in the coding units 1010,depths of coding units 1012 and 1054 are 1, depths of coding units 1014,1016, 1018, 1028, 1050, and 1052 are 2, depths of coding units 1020,1022, 1024, 1026, 1030, 1032, and 1048 are 3, and depths of coding units1040, 1042, 1044, and 1046 are 4.

In the prediction units 1060, some coding units 1014, 1016, 1022, 1032,1048, 1050, 1052, and 1054 are obtained by splitting the coding units inthe coding units 1010. In other words, partition types in the codingunits 1014, 1022, 1050, and 1054 have a size of 2N×N, partition types inthe coding units 1016, 1048, and 1052 have a size of N×2N, and apartition type of the coding unit 1032 has a size of N×N. The partitiontype having the size of N×N may be set only when the coding unit 1032 isa minimum coding unit. Prediction units and partitions of the codingunits 1010 are smaller than or equal to each coding unit.

Transformation or inverse transformation is performed on image data ofthe coding unit 1052 in the transformation units 1070 in a data unitthat is smaller than the coding unit 1052. Also, the coding units 1014,1016, 1022, 1032, 1048, 1050, and 1052 in the transformation units 1070are different from those in the prediction units 1060 in terms of sizesand shapes. In other words, the video encoding and decoding apparatuses100 and 200 may perform intra prediction, motion estimation, motioncompensation, transformation, and inverse transformation individually ona data unit in the same coding unit.

Accordingly, encoding is recursively performed on each of coding unitshaving a hierarchical structure in each region of a maximum coding unitto determine an optimum coding unit, and thus coding units having arecursive tree structure may be obtained. Encoding information mayinclude split information about a coding unit, information about apartition type, information about a prediction mode, and informationabout a size of a transformation unit. Table 1 shows the encodinginformation that may be set by the video encoding and decodingapparatuses 100 and 200.

TABLE 1 Split Information 0 Split (Encoding on Coding unit having Sizeof 2N × 2N and Current Depth of d) Information 1 Prediction PartitionType Size of Transform Unit Repeatedly Mode Encode Intra SymmetricalAsymmetrical Split Split Coding Units Inter Partition PartitionInformation 0 of Information 1 of having Skip Type Type TransformationTransformation Lower Depth (Only Unit Unit of d + 1 2N × 2N) 2N × 2N 2N× nU 2N × 2N N × N 2N × N 2N × nD (Symmetrical N × 2N nL × 2N PartitionType) N × N nR × 2N N/2 × N/2 (Asymmetrical Partition Type)

The output unit 130 of the video encoding apparatus 100 may output theencoding information about the coding units having a tree structure, andthe image data and encoding information extractor 220 of the videodecoding apparatus 200 may extract the encoding information about thecoding units having a tree structure from a received bitstream.

Split information indicates whether a current coding unit is split intocoding units of a lower depth. If split information of a current depth dis 0, a depth, in which a current coding unit is no longer split into alower depth, is a coded depth, and thus information about a partitiontype, prediction mode, and a size of a transformation unit may bedefined for the coded depth. If the current coding unit is further splitaccording to the split information, encoding is independently performedon four split coding units of a lower depth.

A prediction mode may be one of an intra mode, an inter mode, and a skipmode. The intra mode and the inter mode may be defined in all partitiontypes, and the skip mode is defined only in a partition type having asize of 2N×2N.

The information about the partition type may indicate symmetricalpartition types having sizes of 2N×2N, 2N×N, N×2N, and N×N, which areobtained by symmetrically splitting a height or a width of a predictionunit, and asymmetrical partition types having sizes of 2N×nU, 2N×nD,nL×2N, and nR×2N, which are obtained by asymmetrically splitting theheight or width of the prediction unit. The asymmetrical partition typeshaving the sizes of 2N×nU and 2N×nD may be respectively obtained bysplitting the height of the prediction unit in 1:3 and 3:1, and theasymmetrical partition types having the sizes of nL×2N and nR×2N may berespectively obtained by splitting the width of the prediction unit in1:3 and 3:1. The symmetrical partition type of N×N may be set only whena current coding unit of 2N×2N is a minimum coding unit.

The size of the transformation unit may be set to be two types in theintra mode and two types in the inter mode. In other words, if splitinformation of the transformation unit is 0, the size of thetransformation unit may be 2N×2N, which is the size of the currentcoding unit. If split information of the transformation unit is 1, thetransformation units may be obtained by splitting the current codingunit. Also, if a partition type of the current coding unit having thesize of 2N×2N is a symmetrical partition type, a size of atransformation unit may be N×N, and if the partition type of the currentcoding unit is an asymmetrical partition type, the size of thetransformation unit may be N/2×N/2.

The encoding information about coding units having a tree structure mayinclude at least one of a coding unit corresponding to a coded depth, aprediction unit, and a minimum unit. The coding unit corresponding tothe coded depth may include at least one of a prediction unit and aminimum unit containing the same encoding information.

Accordingly, it is determined whether adjacent data units are includedin the same coding unit corresponding to the coded depth by comparingencoding information of the adjacent data units. Also, a correspondingcoding unit corresponding to a coded depth is determined by usingencoding information of a data unit, and thus a distribution of codeddepths in a maximum coding unit may be determined.

Accordingly, if a current coding unit is predicted based on encodinginformation of adjacent data units, encoding information of data unitsin deeper coding units adjacent to the current coding unit may bedirectly referred to and used.

Alternatively, if a current coding unit is predicted based on encodinginformation of adjacent data units, data units adjacent to the currentcoding unit are searched using encoded information of the data units,and the searched adjacent coding units may be referred for predictingthe current coding unit.

FIG. 13 is a diagram for describing a relationship between a codingunit, a prediction unit or a partition, and a transformation unit,according to encoding mode information of Table 1.

A maximum coding unit 1300 includes coding units 1302, 1304, 1306, 1312,1314, 1316, and 1318 of coded depths. Here, since the coding unit 1318is a coding unit of a coded depth, split information may be set to 0.Information about a partition type of the coding unit 1318 having a sizeof 2N×2N may be set to be one of a partition type 1322 having a size of2N×2N, a partition type 1324 having a size of 2N×N, a partition type1326 having a size of N×2N, a partition type 1332 having a size of2N×nU, a partition type 1334 having a size of 2N×nD, a partition type1336 having a size of nL×2N, and a partition type 1338 having a size ofnR×2N. When the coding unit 1318 having the size of 2N×2N is a minimumcoding unit, the information about a partition type may be set to apartition type 1328 having a size of N×N.

Split information (TU size flag) of transformation unit is a type of atransformation index, and a size of a transformation unit whichcorresponds to the transformation index may be changed according to aprediction unit type or a partition type of the coding unit.

For example, when the partition type is set to be symmetrical, i.e., thepartition type 1322, 1324, 1326, or 1328, a transformation unit 1342having a size of 2N×2N is set if the split information of transformationunit is 0, and a transformation unit 1344 having a size of N×N is set ifa TU size flag is 1.

When the partition type is set to be asymmetrical, i.e., the partitiontype 1332, 1334, 1336, or 1338, a transformation unit 1352 having a sizeof 2N×2N is set if a TU size flag is 0, and a transformation unit 1354having a size of N/2×N/2 is set if a TU size flag is 1.

Referring to FIG. 13, the TU size flag is a flag having a value or 0 or1, but the TU size flag is not limited to 1 bit, and a transformationunit may be hierarchically split having a tree structure while the TUsize flag increases from 0. The split information of transformation unitmay be used as an example of the transformation index.

In this case, if the split information of transformation unit is usedtogether with a maximum size of the transformation unit and a minimumsize of the transformation unit, a size of the transformation unit whichis actually used may be expressed. The video encoding apparatus 100 mayencode maximum size information of transformation unit, minimum sizeinformation of transformation unit, and maximum split information oftransformation unit. The encoded maximum size information oftransformation unit, the encoded minimum size information oftransformation unit, and the encoded maximum split information oftransformation unit may be inserted into an SPS. The video decodingapparatus 200 may decode a video by using the maximum size informationof transformation unit, the minimum size information of transformationunit, and the maximum split information of transformation unit.

In an example, (a) if a size of a current coding unit is 64×64, and themaximum size of the transformation unit is 32×32, (a-1) a size of thetransformation unit may be set to 32×32 when the split information oftransformation unit is 0, (a-2) the size of the transformation unit maybe set to 16×16 when the split information of transformation unit is 1,and (a-3) the size of the transformation unit may be set to 8×8 when thesplit information of transformation unit is 2.

In another example, (b) if the size of the current coding unit is 32×32,and the minimum size of the transformation unit is 32×32, (b-1) the sizeof the transformation unit may be set to 32×32 when the splitinformation of transformation unit is 0, and since the size of thetransformation unit cannot be smaller than a size of 32×32, the splitinformation of transformation unit cannot be further set.

In another example, (c) if the size of the current coding unit is 64×64,and the maximum split information of transformation unit is 1, the splitinformation of transformation unit may be 0 or 1, and another splitinformation of transformation unit cannot be set.

Thus, if it is defined that the maximum TU size flag is‘MaxTransformSizeIndex’, a minimum transformation unit size is‘MinTransformSize’, and a transformation unit size is ‘RootTuSize’ whenthe TU size flag is 0, then a current minimum transformation unit size‘CurrMinTuSize’ that can be determined in a current coding unit, may bedefined by Equation (1):CurrMinTuSize=max(MinTransformSize,RootTuSize/(2^MaxTransformSizeIndex))  (1)

Compared to the current minimum transformation unit size ‘CurrMinTuSize’that can be determined in the current coding unit, a transformation unitsize ‘RootTuSize’ when the TU size flag is 0 may denote a maximumtransformation unit size that can be selected in the system. In Equation(1), ‘RootTuSize/(2^MaxTransformSizeIndex)’ denotes a transformationunit size when the transformation unit size ‘RootTuSize’, when the TUsize flag is 0, is split a number of times corresponding to the maximumTU size flag, and ‘MinTransformSize’ denotes a minimum transformationsize. Thus, a smaller value from among‘RootTuSize/(2^MaxTransformSizeIndex)’ and ‘MinTransformSize’ may be thecurrent minimum transformation unit size ‘CurrMinTuSize’ that can bedetermined in the current coding unit.

According to an exemplary embodiment, the maximum transformation unitsize RootTuSize may vary according to the type of a prediction mode.

For example, if a current prediction mode is an inter mode, thenRootTuSize′ may be determined by using Equation (2) below. In Equation(2), ‘MaxTransformSize’ denotes a maximum transformation unit size, and‘PUSize’ denotes a current prediction unit size.RootTuSize=min(MaxTransformSize, PUSize)  (2)

That is, if the current prediction mode is the inter mode, thetransformation unit size ‘RootTuSize’ when the TU size flag is 0, may bea smaller value from among the maximum transformation unit size and thecurrent prediction unit size.

If a prediction mode of a current partition unit is an intra mode,‘RootTuSize’ may be determined by using Equation (3) below. In Equation(3), ‘PartitionSize’ denotes the size of the current partition unit.RootTuSize=min(MaxTransformSize, PartitionSize)  (3)

That is, if the current prediction mode is the intra mode, thetransformation unit size ‘RootTuSize’ when the TU size flag is 0 may bea smaller value from among the maximum transformation unit size and thesize of the current partition unit.

However, the current maximum transformation unit size ‘RootTuSize’ thatvaries according to the type of a prediction mode in a partition unit isjust an example and the present invention is not limited thereto.

FIG. 14 is a flowchart illustrating a method of encoding a video byusing a prediction unit based on coding units having a tree structure,according to an exemplary embodiment.

In operation 1210, a current picture is split into at least one maximumcoding unit. A maximum depth indicating the total number of possiblesplitting times may be predetermined.

In operation 1220, a coded depth to output a final encoding resultaccording to at least one split region, which is obtained by splitting aregion of each maximum coding unit according to depths, is determined byencoding the at least one split region, and coding units according to atree structure is determined.

The maximum coding unit is spatially split whenever the depth deepens,and thus is split into coding units of a lower depth. Each coding unitmay be split into coding units of another lower depth by being spatiallysplit independently from adjacent coding units. Encoding is repeatedlyperformed on each coding unit according to depths.

Also, a transformation unit according to partition types having theleast encoding error is determined for each deeper coding unit. In orderto determine a coded depth having a minimum encoding error in eachmaximum coding unit, encoding errors may be measured and compared in alldeeper coding units according to depths.

When the transformation unit is determined, a transformation unit fortransformation of the coding unit may be determined. The transformationunit according to the present exemplary embodiment may be determined asa data unit to minimize an error incurred by the transformation unit fortransformation of the coding unit.

In each maximum coding unit, a picture is encoded based on a partitiontype that is determined based on coding units according to depths, anddepths of the coding units according to depths, and coding units of acoded depth are independently determined for each of the coding unitsaccording to depths, so that the coding units having a tree structuremay be determined.

In at least one of cases in which a current coding unit is no longersplit into coding units of a lower depth, in which the current codingunit is a maximum coding unit from among current maximum coding units,and in which the current coding unit is a coding unit of a lowest depthfrom among the current maximum coding units, a partition type of thecurrent coding unit may further include a partition having the same sizeas the coding unit of a lower depth. The partition type may includesymmetrical partitions that are obtained by symmetrically splitting aheight or width of the current coding unit, partitions obtained byasymmetrically splitting the height or width of the current coding unit,partitions that are obtained by geometrically splitting the currentcoding unit, or partitions having arbitrary shapes. The predictionencoding may be performed based on the partition type and the predictionmode of a prediction unit with respect to the current coding unit.

Accordingly, in at least one of cases in which the current coding unitis no longer split into the coding units of a lower depth, in which thecurrent coding unit is the minimum coding unit from among the currentmaximum coding units, and in which the current coding unit is the codingunit of a lowest depth from among the current maximum coding units,prediction encoding may be performed by using not only the symmetricalpartitions that are obtained by symmetrically splitting a height orwidth of the current coding unit, the partitions obtained byasymmetrically splitting the height or width of the current coding unit,the partitions that are obtained by geometrically splitting the currentcoding unit, and the partitions having arbitrary shapes but also byusing the partition having the same size as the coding unit of a lowerdepth.

In addition, in at least one of cases in which the current coding unitmay be split into the coding units of a lower depth, in which thecurrent coding unit is not the coding unit of a lowest depth from amongthe current maximum coding units, and in which the current coding unitis the coding unit of a lowest depth from among the current maximumcoding units, intra prediction and inter prediction which are performedby using the partition having the same size as the coding unit of alower depth may be skipped.

In operation 1230, encoded image data constituting the final encodingresult according to the coded depth is output for each maximum codingunit, with encoding information about the coded depth and an encodingmode. The information about the encoding mode may include informationabout a coded depth or split information, information about a partitiontype of a prediction unit, information about a prediction mode,information about a size of a transformation unit, transformation indexinformation, and the like.

Coding unit structure information about a size and a variable depth ofthe coding unit defined according to a data unit such as sequences,pictures, slices, or GOPs may be inserted into a header of a bitstream,a SPS, or a PPS and then may be output. The encoded information aboutthe encoding mode, and the coding unit structure information about thesize and the variable depth of the coding unit may be inserted into theheader of the bitstream, the SPS, or the PPS and then may be transmittedto a decoder with the encoded image data.

FIG. 15 is a flowchart illustrating a method of decoding a video byusing a prediction unit based on coding units having a tree structure,according to an exemplary embodiment.

In operation 1310, a bitstream of an encoded video is received andparsed.

In operation 1320, encoded image data of a current picture assigned to amaximum coding unit, and information about a coded depth and an encodingmode according to maximum coding units, and the coding unit structureinformation about the size and the variable depth of the coding unit areextracted from the parsed bitstream. The information about the codeddepth and the encoding mode, the coding unit structure information aboutthe size and the variable depth of the coding unit, and the splitinformation may be extracted from a header of a bitstream, a SPS, or aPPS.

The coded depth of each maximum coding unit is a depth having the leastencoding error in each maximum coding unit. In encoding each maximumcoding unit, the image data is encoded based on at least one data unitobtained by hierarchically splitting the each maximum coding unitaccording to depths.

According to the information about the coded depth and the encodingmode, the maximum coding unit may be split into coding units having atree structure. Each of the coding units having the tree structure isdetermined as a coding unit corresponding a coded depth, and isoptimally encoded as to output the least encoding error. Accordingly,encoding and decoding efficiency of an image may be improved by decodingeach piece of encoded image data in the coding units after determiningat least one coded depth according to coding units.

The maximum size and the minimum size of the coding unit from among thecurrent coding units having the tree structure may be determined basedon the coding information including at least two of the informationabout the variable depth of the current coding units having the treestructure, the information about the maximum size of the coding unit,and the information about the minimum size of the coding unit.

Also, the transformation units according to the tree structure in thecoding units may be determined based on the transformation index of thecoding information.

A partition type may be determined based on a depth of a current codingunit, and prediction decoding is performed based on the coding units andthe partition type, so that the picture may be decoded. The partitiontype according to the present exemplary embodiment may include at leastone of partitions having the same size as the current coding unit,partitions that are obtained by dividing a height or width of thecurrent coding unit by two, symmetrical partitions that are obtained bysymmetrically splitting the height or width of the current coding unit,partitions obtained by asymmetrically splitting the height or width ofthe current coding unit, partitions that are obtained by geometricallysplitting the current coding unit, and partitions having arbitraryshapes.

In at least one of cases in which the current coding unit is no longersplit into the coding units of a lower depth, in which the currentcoding unit is a minimum coding unit from among current maximum codingunits, and in which the current coding unit is a coding unit of a lowestdepth from among the current maximum coding units, the partition type ofthe current coding unit may further include a partition having the samesize as the coding unit of a lower depth.

In operation 1330, the image data of each maximum coding unit is decodedbased on the information about the coded depth and the encoding modeaccording to the maximum coding units.

A maximum size and a minimum size of the coding units may be read basedon coding unit structure information and split information, and thus thecoding units having the tree structure may be determined. Theinformation about the partition type and the prediction mode of theprediction unit of the coding unit may be read from the informationabout the encoding mode, and prediction decoding may be performed withrespect to the coding units based on the information about the partitiontype and the prediction mode, so that the current coding unit may bedecoded.

For example, in at least one of cases in which the current coding unitmay be split into the coding units of a lower depth, in which thecurrent coding unit is not the coding unit of a lowest depth from amongthe current maximum coding units, and in which the current coding unitis the coding unit of a lowest depth from among the current maximumcoding units, intra prediction or inter prediction/compensation whichare performed by using the partition having the same size as the codingunit of a lower depth may be skipped.

However, in at least one of cases in which the current coding unit is nolonger split into the coding units of a lower depth, in which thecurrent coding unit is the minimum coding unit from among the currentmaximum coding units, and in which the current coding unit is the codingunit of a lowest depth from among the current maximum coding units, theintra prediction or the inter prediction/compensation may be performedby using not only the partitions having the same size as the currentcoding unit, the partitions obtained by dividing a height or width ofthe current coding unit by two, and the partitions obtained byasymmetrically splitting the height or width of the current coding unitbut also by using the partition having the same size as the coding unithaving a depth lower than that of the current coding unit.

The decoded image data may be reproduced by a reproducing apparatus,stored in a storage medium, or transmitted through a network.

An exemplary embodiment can be written as computer programs and can beimplemented in general-use digital computers that execute the programsusing a computer readable recording medium. Examples of the computerreadable recording medium include magnetic storage media (e.g., ROM,floppy disks, hard disks, etc.) and optical recording media (e.g.,CD-ROMs, or DVDs). Moreover, it is understood that in exemplaryembodiments, one or more units and elements of the above-describedapparatuses can include circuitry, a processor, a microprocessor, etc.,and may execute a computer program stored in a computer-readable medium.

While exemplary embodiments have been particularly shown and describedabove, it will be understood by those of ordinary skill in the art thatvarious changes in form and details may be made therein withoutdeparting from the spirit and scope of the present inventive concept asdefined by the appended claims. The above-described exemplaryembodiments should be considered in descriptive sense only and not forpurposes of limitation. Therefore, the scope of the inventive concept isdefined not by the detailed description of exemplary embodiments but bythe appended claims, and all differences within the scope will beconstrued as being included in the present inventive concept.

What is claimed:
 1. A method of decoding a video, the method comprising:receiving a bitstream with respect to an encoded video and parsing thereceived bitstream; extracting, from the received bitstream, coding unitstructure information indicating a size of a coding unit that is a dataunit for decoding of a picture of the encoded video, a variable depth ofthe coding unit, information about a coded depth and an encoding modeindicating one among prediction types including skip mode, inter modeand intra mode from the bitstream; and determining a current coding unitbased on the coding unit structure information, the variable depth ofthe coding unit and the information about the coded depth, when theencoding mode indicates the skip mode, determining a prediction unithaving the same size as the current coding unit; when the encoding modeindicates one of the intra mode and the inter mode, extracting partitiontype information indicating a partition of a prediction unit; when theencoding mode indicates the intra mode, determining a prediction unitincluding at least one rectangular block, from the current coding unit,based on the partition type information; and, when the encoding modeindicates the inter mode, determining a prediction unit including one ofa partition, symmetric partitions and asymmetric partitions, from thecurrent coding unit, based on the partition type information, whereinthe symmetric partitions are obtained by symmetrically splitting atleast one of a height and a width of the current coding unit, andwherein the asymmetric partitions are obtained by asymmetricallysplitting at least one of the height and the width of the current codingunit, wherein: when the information about the coded depth indicates asplit for a current depth, the current coding unit of the current depthis split into coding units of a lower depth, independently fromneighboring coding units, and when the information about the coded depthindicates a non-split of a current depth, the prediction unit isobtained from the current coding unit.
 2. The method of claim 1,wherein, in at least one of cases in which the current coding unit is nolonger split into the coding units of a lower depth, in which thecurrent coding unit is a minimum coding unit from among current maximumcoding units, and in which the current coding unit is a coding unit of alowest depth from among the current maximum coding units, a partitiontype of the current coding unit further comprises a partition having thesame size as the coding unit of the lower depth.